A Novel Pilot Allocation Technique for Uplink OFDMA in ISAC Systems

In integrated sensing and communication (ISAC) systems, pilot signals play a crucial role in enhancing sensing performance due to the strong autocorrelation properties and high transmission power associated with pilot transmission. However, conventional interleaved pilots inherently constrain the maximum unambiguous range and reduce the accuracy of channel impulse response (CIR) estimation compared to continuous orthogonal frequency-division multiple access (OFDMA) signals. To address this challenge, we propose a novel overlapped block-pilot structure for uplink OFDMA-based ISAC systems, referred to as phase-shifted ISAC (PS-ISAC) pilot allocation. The proposed method employs a cyclic prefix (CP)-based phase-shifted pilot design, enabling efficient multi-transmitter pilot separation at the receiver. Simulation results demonstrate that the proposed scheme improves CIR separability, reduces computational complexity, and improves mean square error (MSE) performance under practical power constraints. Furthermore, we show that utilizing continuous pilot resources maximizes the unambiguous range.